In recent years, exploitation of inorganic elements mainly including rare earths has been indispensable. Meanwhile stable supply of rare earths and the environmental impacts by rare earths also pose concerns. Therefore there is a need to develop techniques that allow effective collection of rare earths from nature and for establishment of techniques that allow low-energy, selective and effective recovery and recycling of rare earths contained in a subtle amount in discarded products and waste water.
Methods for recovering rare earths reported are methods in which rare earth elements are recovered by solvent extraction utilizing N,N-dioctyldiglycol amic acid (DODGAA) and the like or by utilizing reducing microorganisms. In addition, peptides that bind to cerium oxide have been described (Patent Literature 1). Peptides that bind to metal oxides such as zinc oxide have also been described (Patent Literature 2). Further, peptides that bind to gold, silver, platinum and the like have been described (Patent Literature 1 and Non Patent Literatures 1 and 2). It has been known that the metal-binding peptides have an ability to form metal nanoparticles under normal temperature by reduction (mineralization activity).
For example, dysprosium is a lanthanoid series rare earth and is a component metal of dysprosium oxide used for permanent magnets in hybrid vehicles and for magneto-optical disks.